Improvements to heat exchange

ABSTRACT

The invention relates to a heat exchanger with inter-connecting cells in a row or block which evenly distribute and transfer heat to a fluid within a cell. Voids between rows or blocks of cells and the heat transfer medium comprise additional means of transferring heat from a heat-transfer medium to the fluid within the cells. The heat exchanger may be used but not limited to applications such as a condenser in an air conditioning unit, a wall heater or an indirect evaporative cooler.

BACKGROUND OF THE INVENTION Field of Invention

This application is based on the Provisional specification filed in relation to New Zealand Patent Application 743830, 743897, 747768, 750809, 750993, 751957, 752163, 752797 and 752948, the entire contents of which are incorporated herein. The invention generally relates to apparatuses and systems that use a means of heat exchange, including a wall or inline heater, an evaporative cooler or an air conditioner.

Description of the Related Art

Japanese patent No 2003-161534 discloses helical protrusions spiralling longitudinally along the inside wall of a pipe and offers an alternative solution of a helical ribbon inside a tube without protrusions. Japanese patent No 2003-161534 also teaches a grouping of hexagonal conduits to store heat.

WO 1985-000212 (Stein) also teaches a grouping of hexagonal conduits for heat storage. Another embodiment of heat exchange is disclosed by FR2435674 (Desmonts) that includes a recess snaking of a mold allowing the introduction and circulation of a heat transfer fluid.

PCT/NZ2013/000185 by the present inventor describes an air conditioning system that draws solar heated air into the building in winter, or alternatively extracts stale air in summer using thermal syphoning boosted by a fan. It comprises conduits with one or more protrusions on the inside periphery of the conduits parallel with the conduit and/or a helical fin extending in a longitudinal direction along the conduits.

This design has been proven to dramatically increase the efficiency of heat extraction from solar heated tubes to air flow compared to a plain tube. This ability to transfer heat from the outside of the tube to the inside can equally be useful to transfer heating from a heat transfer medium other than solar.

Depending on the application, it may be more beneficial in some circumstances for the conduits to be prismatic or at least one pair of parallel sides, where the connectivity of the individual cells of a prismatic geometric shape improves heat transfer compared with reduced points of contact between cells in a rounded surface for example. In a prismatic geometric block, rapid heat exchange can take place between conduits using a heat transfer material.

Hexagonal conduits allow for complete connectivity between conduits without gaps which is very suitable for heat storage. However, for heat exchange purposes, octagonal conduits are advantageous because they create a void between conduits in which a heat exchange medium can be contained fluidly unconnected to the inside of the conduits. These voids can include fins to transfer heat from the medium to the conduits or be shaped in such a way as to maximize contact with the medium.

The number and size of prismatic conduits are scalable to suit specific flow volumes of a fluid or its heat exchange medium. One or more conduits can be manufactured together or they can be manufactured individually or so that they interlock.

Whether prismatic conduits form a block or a single row or whether some of the sides are rounded will depend on the application and the type of heat exchange available. For example, a prismatic block may be a more efficient means of transferring heat where a fluid is passing through a heat exchanger via a primary duct or channel i.e. an inline application. On the other hand, a single row of prismatic conduits may be preferable such as, for example, a wall heater to minimize intruding into a living space.

The heat exchange medium may be on one or more sides of the block or row of prismatic conduits. Alternatively the heat exchange medium may radiate heat from within the block or row of prismatic conduits. The heat exchange medium can for example be etched foil electric heating elements, oil, water, refrigerant in an absorption cycle or other means of heating/cooling.

Apart from maximizing heat exchange between conduits, it is also the objective of this patent to optimize heat exchange to the fluid flowing within one or more prismatic conduits. Therefore, it is preferable for these conduits to comprise protrusions extending longitudinally along the inside periphery wall of one or more conduits. These protrusions function to increase the heated area of the periphery wall. They may be in parallel with the conduit or follow a helical trajectory depending on manufacturing techniques available.

It is preferable to terminate the protrusions such that they outline a cylindrical shaped void within the conduits and that the protrusions are perpendicular to a tangent to the cylindrical shaped void such that the ends of the protrusions are generally evenly spaced. This is especially important with prismatic conduits to avoid uneven and restricted spaces between protrusions.

If one or more conduits also include a rippled helical ribbon, a fluid is allowed to circulate unimpeded along the conduit resulting in a smoother helical fluid trajectory. This helical trajectory through the cylindrical void minimizes flow interruptions which would otherwise occur around the sharper inner angles of a prismatic conduit.

The helical trajectory provided by the rippled helical fin also functions to lengthen the flow path while causing minimum hindrance to flow rate as well as to mix a fluid, thus preventing laminar flow. Further, the helical trajectory maximizes turbulence at the terminals of the protrusions for optimum heat extraction which is another reason why it is preferable for the protrusions to be equally spaced at their ends. The ripples or corrugations in the helix themselves provide further turbulence and mixing.

In terms of assembly, a cylindrical void enables the rippled helical fin to be more easily inserted longitudinally along the inside of the conduit and rotated into position by means of a tab for example. In certain applications, the rippled helical ribbon itself may be a heating element to increase the rate of heating over a certain distance. It could comprise, for example, an etched foil heating element.

Preferably the material of the block or row of prismatic conduits has high thermal conductivity such that rapid heat exchange can take place between conduits. Aluminium is one such material which can also be easily extruded as one or more cell at a relatively low cost. A heat exchange medium may be on one or more sides of a block of hexagonal prismatic conduits.

In the application of air conditioners, standard liquid-to-air heat exchangers are generally made with copper tubes and aluminium fins. Potential weaknesses with this design include damage to fins, galvanic and/or atmospheric corrosion and high pressure drop of air flow according to fin spacing and accumulation of pollution. Heat from the heat exchanger in the condenser is transferred through the copper tube surface to the aluminium fin which is in close contact with the tube at the fin collar. Although copper is a better heat conductor, it's more expensive and heavier, so aluminium is generally the chosen material for the fins, especially for the outdoor unit.

The joint between copper and aluminium is vulnerable to corrosion since two dissimilar metals (copper and aluminium) are brought together into electrical contact with moisture. One of the metals in the couple becomes the anode, in this case the aluminium fins, and corrodes faster than it would all by itself, while the other becomes the cathode and corrodes slower than it would alone. In this case the cathode is the copper tube.

As the aluminium corrodes at the fin collar, the joint between copper and aluminium becomes a copper aluminium oxide joint which has significantly lower heat conductivity than aluminium itself. Providing there is an excellent fin/tube bond, fins provide twice the heat transfer on any coil compared with the coil. So a reduced heat transfer from corrosion at the aluminium collar would significantly reduce efficiency over time.

According to Jay E. Fields PhD in a paper called ‘CORROSION OF ALUMINUM-FIN, COPPER-TUBE HEAT EXCHANGE COILS’, in spite of the presence of the ‘more sacrificial’ aluminum, in most failures of indoor coils, copper tubes will suffer corrosion while there will be little corrosion on the aluminium fins in direct contact due to a direct attack of a corroding agent on the copper.

In fact, pollution on either the copper tube or the aluminium fins will influence heat transfer. Pollution on the fins can limit airflow through the heat exchanger causing a decrease in the temperature difference between the liquid/gas in the copper tube and the air passing over the fins resulting in reduced heat transfer. Furthermore, a layer of pollution on the copper tube will result in corrosion and an increased thermal resistance of the material and therefore a much lower heat transfer.

The design of very closely packed fins makes it difficult to clean off this pollution from the fins or the copper tube. The fins are very thin and so easily damaged during maintenance which leads to further reductions in efficiency.

There is also another issue with closely packed fins. The amount of heat removed in a heat exchanger is directly proportional to 1) the fin surface area and 2) the amount of heat that can be transferred from this area from air flow. Closely spaced fins require a higher pressure to move heated air away from the fins. Boundary layers of stagnant air molecules slow heat removal acting like a blanket to insulate the fin surfaces. These boundary layers on each side of a pair of fins reduce the path of escape for the heated air, so the fin spacing can be significant.

A Thesis Presented to The Academic Faculty By Monifa Fela Wright ‘PLATE-FIN-AND-TUBE CONDENSER PERFORMANCE AND DESIGN FOR REFRIGERANT R-410A AIR-CONDITIONER” demonstrated how COP increased with a decreased depth of the air passage due to a decrease in compressor and condenser fan power.

Much study has been undertaken to optimize the performance of the standard liquid-to-air heat exchanger and to mitigate its vulnerabilities, such as 1) fin fixation (tightly packed aluminium collar on the copper tubes to form a barrier to moisture), 2) fin distance and velocity that influence pollution accumulation, 3) the type of metal and 4) coatings to protect metals. Even so, these have not entirely been resolved. Basically air flow soils any environment but especially in polluted environments, and so this is where the fundamental problems still remain with the basic design.

The current patent is an entirely different approach to heat exchange. It is expected that the following objectives will be met:

-   -   Improved heat transfer to air flow     -   Significant reduction in wasted energy from a condenser fan     -   Reduced power demand on the compressor     -   Ease of access to clean the copper coil and aluminium fins to         remove any pollution     -   Significantly reduced vulnerability to damage     -   Long term efficiency of heat exchange

Another embodiment of a heat exchange design is provided wherein a pipe is twisted to form continuous bends. This design is more suited to an evaporator unit for example. Usually an evaporator heat exchanger comprises a series of adjacent pipes that extend along the length of the evaporator with bends at the end to link them together. Often these are incorporated into fins. Apart from the issues already mentioned, long lengths of pipe followed by sharp bends can cause large pressure drops such that the fluid loses momentum. This can be likened to a car picking up speed along a long straight road followed by a sharp bend.

It is expected that a continuously bending pipe wherein the fluid is constantly mixing at a similar speed would be preferable. The efficiency of heat exchange would be further improved if the type of pipe used is one with spiralling ridges inside and outside the pipe. These pipes, including in copper, are currently available on the market. This design is expected to avoid the need for aluminium fins. This can make cleaning pollution from the pipes much easier.

Fins contribute a large proportion of heat transfer in air conditioning units so it is essential that the pipes in an evaporator are designed in such a way as to compensate for the lack of fins.

Apart from air conditioning, the embodiment of heat exchange of conduits with at least two parallel flat sides is applicable for other apparatus such as a wall or inline heater wherein the prismatic conduit is also more suitable. Depending on such considerations as available space or application, other embodiments of heat exchange include a conduit with flattened opposite sides like an octagonal conduit but with a rounded conduit on the other sides for an indirect evaporative cooler for example.

Evaporative coolers are designed to cool air through the evaporation of water. Generally, evaporative coolers are cheaper to run than heat pumps and so are very attractive in hot climates. There are two types—direct and indirect. With direct evaporative coolers, supply air flow is in direct contact with a wet surface. The problem with direct evaporative cooling is that air needs to be sufficiently dehumidified and then humidified again in order to cool. Without the dehumidifying process, the outdoor relative humidity level needs to be below 30%.

Indirect evaporative coolers exchange cooling with one or more ‘wet’ channels which are cooled by evaporation exchanging cooling with one or more ‘dry’ channels. The ‘wet’ and ‘dry’ channels are fluidly unconnected. Generally indirect evaporative coolers comprise thin parallel heat exchange plates with alternating wet and dry channels. The Maisotsenko Cycle achieves the objective of indirect evaporation by a different means. It drives a proportion of the air flow from the ‘dry’ side through small holes to contribute to evaporation and cooling on the ‘wet’ side. Due to positive pressure applied to the ‘dry’ side, the air flow into the building is not humidified.

However, these plates can cause excessive restriction of air flow increasing pressure. Holes easily clog up resulting in increased fan energy required to push the air flow through. They also require periodic replacing as they block up over time which can be expensive.

The extent of cooling achieved depends largely on relative humidity in the air. In order to enable evaporative cooling to have greater geographical reach, there needs to be an efficient dehumidifying process prior to evaporative cooling. The ideal heat to dry air is between 60 and 80 degrees with the resulting relative humidity of this air being preferably under 30%.

This range can be achieved by heating air prior to entering the evaporative cooler in an effort to extend the geographical reach of evaporative cooling. Solar air collectors connected to the air supply of the indirect evaporative cooler is one way to dehumidifies air with heat prior to supplying the indirect evaporative cooler. They can provide the ideal heat of 60+C to dry air.

The current patent puts forward a system and a compact means of efficiently transferring heating or cooling to air flow, that reduces the required fan pressure to drive the air through, and can have greater geographical reach,

SUMMARY OF THE INVENTION

Preferably a row of conduits comprise a conduit with at least two flat parallel sides in contact with another conduit

Preferably the conduits comprise one or more protrusions extending longitudinally on the inside surface of the one or more conduits

Preferably the length and/or spacing of the protrusions optimize heat transfer to a fluid. Preferably the one or more protrusions on the inside surface of the conduit radiate to the centre of the conduit

Preferably the ends of the protrusions outline a cylindrical shaped void,

Preferably the one or more protrusions are perpendicular to a tangent to the cylindrical shaped void such that the ends of the protrusions are generally evenly spaced

Preferably the conduits comprise a rippled helical ribbon extending longitudinally inside the one or more prismatic conduits.

Preferably the rippled helical ribbon is removable

Preferably the rippled helical ribbon includes tabs that lock it into positon between the protrusions

Preferably the rippled helical ribbon comprises a heating element

Preferably the conduits comprise a heat source in dose proximity and/or in contact with the conduits to encourage an even distribution of heat to all parts of the prismatic block Preferably a block of conduits comprises a void between conduits comprising a heating element or pipe for a heat exchange medium in close proximity and/or in contact with the conduits

Preferably the void created between he conduits with parallel flat sides, comprises fins to transfer heat from the medium to the conduits

Preferably the void between conduits is shaped in such a way as to maximize contact with the medium.

Preferably a row of conduits comprises heating on one or more sides of the outside perimeter and in close proximity and/or in contact with the prismatic conduits

DEATILED DESCRIPTION OF THE INVENTION

FIG. 1 discloses a perspective view of an example of a heat exchanger 23 comprising two rows 2 of conduits 1 that form a block. Protrusions 3 extend longitudinally along the inside periphery of conduits 1. The outer perimeter comprises flat face 4 which enables improved proximity and/or points of contact with other octagon cells thereby improving heat exchange.

The advantage of a block of octagonal conduits as compared to other prismatic conduits in certain applications is that the outer perimeter is spatially compact when accommodated in a square or rectangular insulating cover. Furthermore, it provides a flat surface if the source of heating is along one or more sides of a block of conduits. Also, in the case of a block of conduits that are octagonal, void 8 is formed by adjoining conduits. This allows for an even distribution of heat exchange when void 8 comprises a heat transfer medium 61. If the material chosen has high thermal conductivity, then heating can evenly radiate to all octagonal faces 4 within the block of octagonal conduits.

The means 5 within void 8 that transfers heat from the medium to the conduits can vary according to the form of heat exchange. It may form a solid surface around the heat source or it may comprise fins extending towards the heat source. Preferable heat transfer means 5 maximizes contact between conduits 1 and the heat exchange medium in order to optimize heat exchange.

If void 8 contains a copper pipe and the extrusion is aluminium, for example, it would be preferable for the pipe to be in contact with the extrusion to maximize heat transfer. This however can cause problems due to unlike metals and corrosion. One possible solution can be, for example, to encase the pipe in two layers of graphene which can prevent this.

Screw port 6 is an example of a way to fasten one or more blocks of prismatic conduits to an end plate, but methods could also include, for example, male and female locking devices between blocks of prismatic conduits. Screw port 7 can be useful to fastening a seal to prevent a fluid entering void 8.

FIGS. 2a and 2b are perspective views of a section of helical fin 9 that can be inserted into the prismatic conduits preferably such that the side edges of helical fin 9 are in contact with protrusions 3. This lengthens the flow path to enable more heat exchange to take place without impeding the flow. It also creates turbulence around the inside periphery of the conduit. It can include side tabs so that it locks into place between the extrusions. Helical fin 9 can be heated. Examples of methods of heating the helical fin include an etched foil heating element or a heated tube 10. If the fin incorporates an etched foil heating element then it could then be corrugated or rippled in order to twist into a helix. Preferably the material of the helix is thermally conductive. Preferably also the etched heating element foil is protected from electricity leakage such as by means of graphene or micathermic sheets.

FIG. 3 is a perspective view that discloses an example how two different materials can form a block of conduits 1 for heat exchanger 23. For example, an outer casing 11 can be a material such as magnesium oxide which forms sides 4 a of conduits 1, with the remaining sides 4 b formed by an extrusion in another material such as aluminium. A means of heating 12 a can be encased and transfer heat from tubular elements or other form of heating to the fluid flowing within conduits 1. Heating means 12 b in void 8 may be in addition or instead of heating means 12 a.

FIG. 4 is a perspective view of another embodiment of heat exchanger 23 comprising conduit 1 in a row of conduits 2. Heating means 13 can be located in close proximity to conduit 1. In this example, heating means 13 comprises etched foil heating elements located on the inside face of heated sheet 14 in the gaps between heated sheet 14 and prismatic conduits 1. The heat transfer medium 61 could also be water pipes or other heat transfer mediums 61. Preferably to avoid electricity leakage, heat transfer strips 15 can be in direct contact with heated sheet 14 and octagonal face 2 to increase the rate of heat exchange with face 4. A means of insulation can be included such as air gap 16 and insulation layer 17 to minimize heat loss away from the conduits.

FIG. 5 is a perspective view of a portion of prismatic conduit 1. This is an example of outer protrusions 18 extending from the outer periphery of conduit 1 wherein the objective is to maximize heat storage outside conduit 1 within cavities 19 and beyond. Inner protrusions 3 may also extend from the inner periphery of wall 2 and/or a helical ribbon extend longitudinally along conduit 1 thereby contributing further to improved heat transfer to a heat storage medium outside conduit 1.

FIG. 6 is a perspective view of an inline heat exchanger 101 of heat exchanger 23 as a block of conduits 1 connected to ducts at duct connections 102 and 103 via reducer 21. In this way a fluid flowing through a duct can be efficiently heated within the inline heat exchanger 101 with insulation and/or cover 20. The number and size of blocks of prismatic conduits can vary according to the duct size. To minimize labour costs, conduits can be extruded as a block of conduits, for example four prismatic conduits 1.

FIG. 7 is a perspective cross-sectional view of heat exchanger 23. This type of heat exchanger could be useful for a condenser in an air conditioner for example. The design of a block of prismatic conduits maximizes inter-connectivity between one or more conduits 1 while also evenly distributing void 8 which comprises a pipe 22 for a heat transfer material 61 such as a refrigerant for example. Preferably heat exchanger 23 is thermally conducting such as aluminium. Protrusions 3 extending longitudinally along octagonal conduit 1 can significantly increase heat exchange from pipes 22 to a fluid flowing through conduits 1. They are shown here to extend in parallel with conduit 1. However, with some manufacturing techniques such as 3D printing, it may be possible for them to also follow a helical trajectory.

One or more fins 24 between pipe 22 and conduit 1 or other means 5 of heat transfer also serve to exchange heat. For example, a means 5 to transfer heat can be shaped to a conduit as shown in FIG. 1 or it can be made from a different heat conductive material than heat exchanger 23. Means 5 within void 8 to transfer heat from a heat transfer medium 61 to the conduits will depend , for example, on the size and shape of the heat transfer medium 61. Removable helical fins 9 can be inserted into the conduits to improve turbulence and heat exchange with the inner periphery of the conduit wall.

This design helps to protect heat exchange pipe 22 from pollution. A coating on pipe 22 or the part of the heat exchanger in contact with pipe 22 can protect from corrosion due to dissimilar metals. For example, a coating of a double layer of graphene is known to not only have exceptionally high thermal conductivity but also to protect from metal corrosion on copper pipes.

Furthermore, conduit 1 which is exposed to constant air flow can be easily accessed and cleaned. The remaining areas of pipe 22 are also easily accessible to clean. Pipe 22 can contain a refrigerant or water for example.

FIG. 8 is a perspective view of one end of heat exchanger 23. It describes an example of ways to seal the cavity that encloses pipe 22 by means of one or more end caps 25. These can be fastened to conduits 1 by means of screw port 6.

FIG. 9 is a perspective view of an example of an arrangement of some of the components for a condenser in an air conditioning unit 65 comprising heat exchanger 23 and fan 39. Fan 39 with motor 29 can be, for example, the type of helical fan described in PCT/NZ2018/050010 which has excellent flow rate and pressure. It is shown here as a helical fan of opposite chirality with two exhaust openings 27 at both ends and an intake opening 28. Alternatively another type of fan could be used such as a centrifugal fan. In this example, intake opening 28 is connected to heat exchanger 23 so that fan 39 draws air through heat exchanger 23. A cover and seal can allow air to be drawn from the fan intake only, thereby increasing the flow rate through heat exchanger 23. Grill 30 can be spaced off blocks of conduits 1 to maximize air flow. In another embodiment one or more heat exchanger 23 can be located at the fan outlet such that the fan is driving air through heat exchanger 23 located at one or more fan exhaust openings 27.

This arrangement would be applicable to an outdoor condenser unit for example. All these components would of course be contained within an outdoor unit along with all other components such as a compressor.

FIG. 10 is a side profile of an example of a grill 32 with drip seal 33. This can be located in front of blocks of conduits 1 that form the heat exchanger. Top of grill 31 and bottom of grill 34 are curved such that the distance 35 is less than the distance 36.

FIG. 11 is a perspective view of an evaporator 105 comprising an example of a refrigerant pipe 38 coiled over the intake opening 40 of a fan 41 comprising a rotor and casing. Fan 41 can also be the type of helical fan as described in PCT/NZ2018/050010 with intake opening 40 and exhaust openings 27 which has excellent flow rate and pressure. Alternatively it can be a standard cross flow fan as commonly used in evaporator units.

In this example, refrigerant pipe 38 coils backwards and forwards over at least intake opening 40 of fan 41 in a FIG. 8 pattern. The refrigerant pipe 38 coils are angled such that it comprises an upper layer 42 and a lower layer 43. The objective is to space refrigerant pipe 38 in such a way as to maximize contact between refrigerant pipe 38 and the air flow without the use of traditional fins to transfer heat. Preferably the spacing allows for easy cleaning of refrigerant pipe 38. Two or more rows of fans 41 can supply the air flow and thermal comfort required with a continuation of refrigerant pipe 38 over intake 40 of the adjoining fan 41. Where there is little air flow between fans 41, refrigerant pipe 38 can discontinue to coil backwards and forwards. It would simply bridge the sections of coiling refrigerant pipe 38.

FIG. 12a is a perspective view of an embodiment of a row 2 of conduits 1 fastened to an upper and lower end plate 44. One or more sides comprise a heat exchange medium 61. An example of an application for this embodiment is disclosed in FIGS. 12b and 12c showing a wall-mounted heat exchanger. Upper portion 63 can include one or more rows 2 of conduits 1, heat exchange medium 61and end plates 44 enclosed in insulation 53 with air gap 58 and casing along with upper opening 47 and controls. Lower portion 49 can be joined to upper portion 63. A front cover 48 can be removed for example via clips and hinging tabs 54 to access a filter tray 55. In a less polluted environment, filter tray 55 may be a washable pre-filter. FIG. 12c is an example of the back of the wall-panel heat exchanger of FIG. 12b showing a means of fastening 52 to the wall. In this example, air is shown to be sourced externally via duct 50 and cowl 56.

FIG. 13 is a cross sectional view of this embodiment of lower portion 49. It discloses filter tray 55, clip 54 to lock a cover in place, duct 50 and cowl 56. Lower portion 49 may also contain a fan in a location within either lower portion 49 or duct 50. It is expected that some passive flow will result from heating air in upper portion 63, but lower portion 49 may also contain a fan to aid flow or to supply fresh air when heating is not needed.

In some environments that are polluted, fresh air requires a higher level of filtration. This necessarily entails increasing the surface area of the filter and fan power. This would require extending the lower portion 49 to include a large filter.

In some applications, it may be preferable to source and clean stale air. FIG. 14a is a perspective view of a wall-mounted heater with an extended lower portion 49. It includes vents 59 such as those shown in FIG. 14 b.

FIG. 14b is a cross sectional view of an example of a lower portion 49 with an increased surface area for filter 70. Of course higher filtration requires a fan 71 capable of handling greater pressure such as a cross flow fan. A helical cross flow fan of the type described in PCT/NZ2018/050010 by the present inventor has been shown to be capable of relatively high pressure and flow rate.

In other embodiments of the invention, whether as blocks or single row of conduits, a fluid other than air, such as water or oil, can be heated by means of the heat exchanger described herein.

FIG. 15a is a perspective cross-sectional view of an indirect evaporative cooler 94 comprising a series of rows 2 of conduits 1. The extent of cooling achieved depends largely on the achieved temperature to dry the air. The ideal heat to dry air is between 60 and 80 degrees and ideally the relative humidity of this air should be under 30%. For this reason, indirect evaporative coolers only work in hot dry areas. They also can use a lot of water which can be a problem in hot dry areas. So in order to widen the geographic reach of evaporative coolers, they need a source of heating to dry air such as solar air heating working in tandem with the indirect evaporative cooler so that they will work when located in hot areas where water, fresh or sea water, isn't an issue.

A solar air collector such as the one described in PCT/NZ2013/000185 is ideally suited to provide free heat to dry air before it is cooled by means of evaporation. A test of a prototype solar air heater reached 60 C at the outlet providing about 350 m3/hr through natural thermal siphoning. The outside temperature was 25 C, so it is expected the temperature and air flow would increase much further as ambient temperature increased.

FIG. 15a discloses how a portion 72 of air conduit 83 can dry a section of desiccant wheel 73 as it slowly rotates. This air then passes through cavity 74 where it can either be exhausted to outside or alternatively mix with fresh air flow from opening 75. Fresh air from opening 75 passes through cavity 74, through desiccant wheel 73 where it is dried and then via conduits 1 which form the heat exchanger along air conduit 77 where it is cooled. Cooled air from air conduit 77 then passes through duct 78 to supply cooled air 79 to the building.

The other portion 80 of air conduit 83 flows through vents 97 in sump 81 and between rows 2 of conduits 1. An opening at close proximity to lid 82 allows moist air to be exhausted to the outside via air conduit 83.

Water can be pumped up through pipes 85 where is it is sprayed or drips onto pad 88 in physical contact with the outside of the rows 2 of conduits 1. This pad 88 can be water-wicking material that holds water while it evaporates cooling as it flows along air conduit 83. It can be held to the cylindrical sides of the row 2 of conduits 1 by, for example, a series of interconnecting vertical ribs that follow the contour of the cylindrical sides of a row 2 and can be pulled out as one allowing easy replacement of the pad 88. These vertical ribs should still allow air to flow upwards in the gaps between pads 88 of alternate rows 2. In this application, evaporative cooling from water functions as the heat exchange medium 61.

FIG. 15b is a cross sectional view 89 from FIG. 15a of a row 2 of conduits 1 with flat parallel sides 4. Sides 4 are in physical contact and may contain means of interlocking such as male and female locks 92 and 93. Cylindrical opposing sides 91 allow water in the pads 88 to evenly distribute as it flows down the sides of rows 2 of conduits 1.

FIG. 16 is a cross-sectional perspective view of an example of an indirect evaporative cooler 94 disclosing rows 2 of conduits 1 spaced apart so that air conduit 83 fluidly connects duct 84, cavity 99, vents 97 above the water line in sump 8, voids 98 between rows 2 of conduits with water wicking material 88 or between a row 2 of conduits and an insulating side 95, and finally to the outside under lid 82. A pump supplies water from pipe 96 to pipes 85.

This compact design is an example of an indirect evaporative cooler which should economize on water compared with other evaporative coolers. This can be significant for regions where water is in short supply. It can use rain water, or sea water if corrosion is not an issue. Any water that is not used drips back into the sump to be used again. It can also incorporate a PV panel, such as on top of lid 82, in order to run a fan and pump so that it functions entirely independently from the electricity supply.

The invention may be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, in any or all combinations of two or more of said parts, elements or features. Where in the foregoing description reference has been made to integers or components having known equivalents thereof, those integers are herein incorporated as if individually set forth.

It should be noted that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. For example, the heat exchange medium can be changed to cool rather than heat or vice versa. Such changes and modifications may be made without departing from the spirit and scope of the invention and without diminishing its attendant advantages. It is therefore intended that such changes and modifications be included within the present invention. 

1. A heat exchanger (60) comprising: at least a first and a second conduit (1) of at least a first row (2); each conduit (1) comprising at least eight sides (4); wherein the internal angles of the conduits (1) are obtuse; each conduit (1) comprising a first fluid flowing within the conduit (1); a first means of heat transfer comprising one or more protrusions (3) extending longitudinally along the inside periphery of the conduit (1); the first and second conduits (1) characterized by: a first side (4) of the first conduit (1) substantially opposite a second side (4) of the first conduit; wherein the first side of the first conduit (1) of conduit 1 is in substantially continuous contact with the second side (4) of a second conduit (1) for at least substantially an eighth of the perimeter of the conduit (1); wherein the shared heat transfer length along both heat transfer lengths of the first and second conduits(1) is constant; a third side of the first conduit (1) adjacent to the first side of the first conduit and a fourth side of the second conduit adjacent to the third side of the first conduit; a heat transfer medium (61); wherein when forming a row of at least two conduits (1), the external surfaces of the third, fourth or more adjacent sides to the third or fourth side and a tangent to the external surface of the conduit (1), the tangent being perpendicular to the first or second side, create a void (8) in thermal contact with the heat transfer medium (61); a second means of heat transfer (5) within void (8); wherein the second means of heat transfer (5) is one or more fins, or thermal mass extending from, or In contact with, the external surfaces of the third, fourth or more sides excluding the first and second sides of conduit (1); wherein the void (8) is blocked from the first fluid.
 2. A heat exchanger (60) as claimed in claim 1 for use in a heater (64) in a building (62), comprising: at least one row (2) of the conduits (1) comprising: a first end (45) and a second end (46); wherein the at least one row (2) is fastened to a first end plate (44) at the first end (45); wherein the void (8) is blocked from the first fluid by at least the first end plate (44) or an end cap (25) wherein the conduit (1) comprises eight sides wherein a fifth and a sixth sides (4) are substantially perpendicular to the first side of the conduit (1); wherein the fifth side is opposite the sixth side; wherein at least one of the fifth or the sixth sides (4) are In thermal communication with the heat transfer medium (61); and wherein the first end portion (49) comprises: a first air entry conduit fluidly connecting the first end (45) of the at least one row (2) to the outside air; a first interior air conduit fluidly connecting the second end (46) of the at least one row (2) to the inside of the building (62).
 3. A heat exchanger (60) as claimed in claim 1 for use in an Indirect evaporative cooler (94) wherein the indirect evaporative cooler (94) comprises: the one or more conduits (1) arranged substantially horizontally; wherein at least the first and second conduits (1) are vertically aligned in row (2); wherein the sides of the one or more conduits (1), excluding the first and second sides, define a substantially cylindrically shaped side (91) to one side of the first and second sides of the conduit (1) in contact with the heat transfer medium (61); wherein the heat transfer medium (61) is water; one or more rows (2) of the conduits (1); and wherein one or more rows (2) are positioned below one or more water pipes (85) and above a sump (81); the sump (81) comprising one or more air vents (97) extending above the water line of the sump (81); a second void (98) between rows (2) of the conduits (1) and the first void (8); a first air supply (84) fluidly connecting the one of more air vents (97) and the second void (98) between rows (2) to a means of heating air; a first exhaust air conduit (83) fluidly connecting the second void (98) to the exterior above the indirect evaporative cooler (94); a second air supply (75) fluidly connecting the interior (77) of the conduits (1) to the exterior; a second exhaust duct (78) fluidly connecting the interior (77) of the conduits (1) to the building interior. 